1. Field of the Invention
The present invention relates to brake shoe supports for railway vehicles and, more particularly, relates to a brake shoe support permitting a degree of lateral movement of an associated brake shoe to track the lateral movement of a wheel on a railway vehicle truck frame.
2. Description of Related Art
It is well known that there is some periodic lateral movement of a railway truck relative to the truck wheels as, for example, the railway vehicle operates in a curved section of track. In certain early patents, brake hangers are disclosed that bend to permit limited lateral movement of the brake shoes during braking relative to a truck frame to which the hangers are pivotally secured. Such a bendable brake hanger is disclosed, for example, in the U.S. Pat. No. 1,166,521 to Hoke. The brake hanger according to this patent is formed of bar stock in the shape of a closed or an open link, with the laterally spaced sides of the brake hanger being forged to be substantially flat for bending more readily in response to lateral movement of the truck frame relative to the wheels. Such repeated bending tends to crystalize the sides of the brake hanger causing them to create a safety hazard by breaking and permitting the brake rigging to drop on the railway in front of a wheel to possibly cause derailment. These shortcomings are discussed in U.S. Pat. No. 1,509,907 to Schaefer, which provides an improved structure in the form of an articulated brake hanger which requires ball joint connections at the upper and lower ends of the brake hanger to prevent bending of substantially rigid laterally spaced side arms of the brake hanger. These ball joint connections, however, require extra maintenance, and may themselves be sources of breakage upon the freezing up of the joints, and the like.
In U.S. Pat. Nos. 5,277,280; 5,242,037; and 5,240,091, all to Stjärne, a brake hanger is disclosed having a pivot joint comprised of a left support washer, a bushing, and a right support washer. This joint allows two depending hangers to freely rotate or swing and pivot in the direction for applying a brake block on a wheel tread, and in the direction for following a sideways motion of the wheel.
U.S. Pat. No. 4,630,714 to Stjärne et al. discloses a brake block holder that engages an axially moveable wheel. The brake block holder is laterally moveable relative to a brake actuator during braking by means of a pair of pivot hangers, each consisting of a stack of leaf springs.
U.S. Pat. No. 4,406,444 to Bogenschutz discloses a brake hanger comprising an upper lug, a lower lug, and an intermediate leaf spring arrangement. The leaf springs are laterally connected by a bar of resilient material to allow lateral movement of the lower lug relative to the upper lug. U.S. Par. No. 3,643,766 to Roush, Jr. discloses a multiple axle railway vehicle truck that includes brake rigging having a stabilizing means which is resiliently yieldable to permit any of the brake shoes to be deflectable outwardly when they are contacted by their respective wheel flanges upon a sufficient lateral movement of their respective wheel axles.
While brake hangers are known that permit limited lateral movement of the brake shoes during braking relative to a truck frame, improvements in the field of brake hangers that are flexible laterally to accommodate greater lateral movement of a brake shoe are still desirable.